<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
     <input type="text" id="inp" onclick="alre()">
</body>    
    <script>
    //练习:取消事件removeEventListener
    var input = document.getElementById("inp");
    input.onmouseover=function(){
    input.onfocus = function () {
        alert('获得焦点');
        
        
    }
    input.onblur = function () {
        alert('失去焦点');

    }
}
    input.onmouseout=function(){
        input.onfocus=function(){};
        input.onblur=function(){};
    }
  
    </script>

</html>